1. Field of the Invention
This invention relates to a semiconductor light-emitting device and, more particularly, to a semiconductor light-emitting device which has high light-extraction efficiency.
2. Description of the Prior Art
In general, semiconductor light-emitting devices (e.g., light-emitting diodes) have been widely used in many application fields, such as key switch systems, back light modules of cell phones, vehicle lighting systems, decorative illuminations, and remote-controlled devices. In order to ensure higher functional reliability and lower energy consumption of semiconductor light-emitting devices, the external quantum efficiency of the semiconductor light-emitting device needs to be well dominated.
In theory, the external quantum efficiency of the semiconductor light-emitting device relates to its internal quantum efficiency and its light-extraction efficiency. And, the external quantum efficiency is determined by properties and quality of material; the light-extraction efficiency refers to the radiation ratio of the radiation emitted from the internal part of device to air or to the encapsulation material (i.e. epoxy resin). Moreover, the light-extraction efficiency is determined by the consumption that is generated while the irradiation is emitted out of the device. One of the reasons of the consumption is that the semiconductor material of the surface layer formed on the device has high refraction coefficient, which forms total reflection on the surface of the material and then makes light unable to be emitted outward. Accordingly, if the light-extraction efficiency rises, the external quantum efficiency of the semiconductor light-emitting device raise as well.
Please refer to FIG. 1. FIG. 1 is a schematic diagram illustrating a light-emitting diode 1 of prior arts. As shown in FIG. 1, the light-emitting diode 1 comprises a substrate 10, N-type GaN 12, P-type GaN 16, a light-emitting region 14 and electrodes 18. In order to electrically connect the P-type GaN 16 and the N-type GaN 12 to operate the light-emitting diode 1, one of the electrodes 18 is formed on the P-type GaN 16 and another electrode 18 is formed on the N-type GaN 12. Before forming the another electrode 18, the light-emitting diode 1 needs to partially etch the P-type GaN 16, the light-emitting region 14, and the N-type GaN 12 by etching processes. Then, another electrode 18 is formed on the exposure part of the N-type GaN 12. However, because the light-emitting region 14 is partially etched, not only the emitting area of the light-emitting diode 1 reduces, but also the light-emitting efficiency decreases, as shown in FIG. 1.
Although various kinds of light-emitting diodes are disclosed nowadays, how to increase the light-extraction efficiency of light-emitting diodes and how to enable the light-emitting diode to emit wide and uniform light are always popular. Accordingly, the scope of the invention is to provide a semiconductor light-emitting device to solve the above-mentioned problems.